#include "base64.h"

static const std::string base64_chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
										"abcdefghijklmnopqrstuvwxyz"
										"0123456789+/";

bool is_base64(unsigned char c) {
	return (isalnum(c) || (c == '+') || (c == '/'));
}

std::string base64_decode(std::string const& encoded_string) {
	int in_len = encoded_string.size();
	int i = 0;
	int j = 0;
	int in_ = 0;
	unsigned char char_array_4[4], char_array_3[3];
	std::string ret;
	
	while (in_len-- && ( encoded_string[in_] != '=') && is_base64(encoded_string[in_])) {
		char_array_4[i++] = encoded_string[in_]; in_++;
		if (i ==4) {
			for (i = 0; i <4; i++)
				char_array_4[i] = base64_chars.find(char_array_4[i]);
			
			char_array_3[0] = (char_array_4[0] << 2) + ((char_array_4[1] & 0x30) >> 4);
			char_array_3[1] = ((char_array_4[1] & 0xf) << 4) + ((char_array_4[2] & 0x3c) >> 2);
			char_array_3[2] = ((char_array_4[2] & 0x3) << 6) + char_array_4[3];
			
			for (i = 0; (i < 3); i++)
				ret += char_array_3[i];
			i = 0;
		}
	}
	
	if (i) {
		for (j = i; j <4; j++)
			char_array_4[j] = 0;
		
		for (j = 0; j <4; j++)
			char_array_4[j] = base64_chars.find(char_array_4[j]);
		
		char_array_3[0] = (char_array_4[0] << 2) + ((char_array_4[1] & 0x30) >> 4);
		char_array_3[1] = ((char_array_4[1] & 0xf) << 4) + ((char_array_4[2] & 0x3c) >> 2);
		char_array_3[2] = ((char_array_4[2] & 0x3) << 6) + char_array_4[3];
		
		for (j = 0; (j < i - 1); j++) ret += char_array_3[j];
	}
	
	return ret;
} 